Conventionally, there has been proposed a working-gas-circulation-type hydrogen engine in which hydrogen, oxygen, and argon gas serving as a working gas are supplied to a combustion chamber; hydrogen is burnt; and the working gas contained in an exhaust gas from the combustion chamber is circulated to the combustion chamber through a circulation passage. Since argon gas is higher in ratio of specific heats than air, the hydrogen engine that uses argon gas as a working gas can be operated with high thermal efficiency.
Meanwhile, when hydrogen is burnt and combined with oxygen, water vapor is generated. Water vapor is in the form of molecules each composed of three atoms (triatomic molecules) and is thus lower in ratio of specific heats than argon gas, which is in the form of molecules each composed of a single atom (monatomic molecules). Accordingly, in the case where the working gas contained in the exhaust gas from the combustion chamber is circulated to the combustion chamber through the circulation passage, elimination of contained water vapor from the gas to be circulated (hereinafter, may be referred to as “circulation gas”) is desirable. Accordingly, a conventional hydrogen engine has a condenser within a circulation passage; the condenser separates (eliminates) contained water vapor from the circulation gas through liquefaction or condensation; and a gas, obtained by the separation of water vapor in the form of condensed water from the circulation gas, is resupplied to the combustion chamber (refer to, for example, Japanese Patent Application Laid-Open (kokai) No. H11-93681).